This invention is directed to a system for measuring the Q spacing between the inside surface and shadow mask of a kinescope faceplate panel.
The screen of a color television picture tube is composed of three phosphors which individually emit red, green and blue light when impacted by electrons. Three electron beams individually energize the three phosphors to produce the desired color of light. The electron beams are caused to impact the desired light emitting phosphor by a color selection electrode, which is commonly called a shadow mask. The shadow mask is a thin metal electrode, which is biased at a high voltage to attract the electron beams, and includes a large number of small apertures through which the electrons pass prior to impacting the various phosphors. The electrons cross over while passing through the shadow mask apertures and in this manner are directed to the proper phosphor so that the "blue" electron beam impacts only the blue phosphor, etc. Because the electron beams cross one another, the spacing between the surface of the shadow mask and the phosphor screen is critical. This spacing is commonly called the Q spacing and must fall within a given range in order to insure that each electron beam impacts only the proper phosphor.
Because the Q spacing is critical in a panel it is common practice to measure the spacing to assure that it falls within the operative tolerance range prior to fully processing the panel and assembling the panel into a tube. Typically, in the prior art the Q spacing is measured by removing the shadow mask from the panel and placing a measuring device into the panel. The shadow mask is reinserted and causes readings on a number of gauges within the measuring device to measure the Q spacing at various locations along the surface of the panel to which the phosphor screen is subsequently applied. After the readings are taken, the shadow mask is removed to permit removal of the measuring device, after which the shadow mask is reinserted. This measuring technique is disadvantageous for several reasons. One of the more important reasons is the need to remove the shadow mask to allow insertion and removal of the measuring devices. Also, the measuring devices contact the surface of the shadow mask, frequently resulting in denting or scratching the fragile shadow mask. For these reasons there is a need for a system for measuring the Q spacing of a kinescope panel without the need for removing the shadow mask from the panel and without abrading the shadow mask to avoid all possibility of scratching or denting the shadow mask. The present invention fulfills these long-felt needs.